Although I haven't used it to trim clips (I have QT Pro), MPEG Steamclip is free and can do the job. It's also a pretty good video swiss army knife to have around for various other video editing-related chores that QT Pro can't do.

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.